textproduct: Albany

WHAT HAS CHANGED

Few significant changes were made with this forecast update compared to the previous. In collaboration with our neighboring offices, we continued to blend NBM90th percentile with the NBM for winds and wind gusts mainly Saturday through Sunday given clear signals for an under-performance by straight NBM. Additionally, we also blended in NBM25th percentile for temperatures Friday night through Sunday night given further increased confidence in dangerously cold temperatures that will also fall below what the NBM alone was producing.

One important thing to point out, however, is that while moderate to high confidence still exists in the dangerous cold outbreak this weekend, guidance has indicated a trend towards a slower onset of snow showers Friday afternoon/Friday evening from the preceding clipper. This should mitigate wind chill values widely reaching dangerous levels Friday night, if at all.

KEY MESSAGES

1) Low to medium probabilities (~10 to 40%) for minor impacts across eastern New York and western New England Friday evening through Saturday evening due to widespread light snow resulting from a clipper system.

2) Moderate to high confidence in a period of dangerously cold conditions across all of eastern New York and western New England that will greatly increase the risk of frostbite and hypothermia this weekend and potentially into early next week.

DISCUSSION

KEY MESSAGE 1...

The next best chance for widespread precipitation comes late Friday afternoon/Friday evening through Saturday afternoon with snow showers expected to overspread the region as a result of a clipper system.

By Friday afternoon, an upper-level cyclone will become positioned near the Hudson/James Bay area, extending a neutrally-tilted shortwave trough southward into the Eastern Great Lakes. Just ahead of this main axis, a secondary, weak shortwave embedded within the mean flow aloft will begin to approach the region, potentially initializing an first batch of light snow showers across portions of the region by Friday afternoon/evening. The uncertainty here is allocated to the location and development of an area of weak surface low pressure just ahead of or along the arctic front associated with the primary surface low well to our north, also located near the Hudson/James Bay area. With this being a relatively moisture-starved system already, that increased surface convergence and subsequent lift would certainly help to moisten the column and at least allow some snow showers to begin in portions of the Southern Adirondacks and possibly the Eastern Catskills where orographic enhancement due to easterly to southeasterly flow could be sufficient to allow precipitation to reach the ground. Most of the medium-range guidance does indicate this are of low pressure developing and sinking far enough south that it does extend into our CWA.

Directly in the wake of the first shortwave comes the second, primary shortwave that looks to deepen as it rotates through our region. This deepening aloft looks to translate to a surface response of cyclogenesis of that area of low pressure initially just along the international border overhead. Snow showers will then be reinforced across the region, especially across higher terrain courtesy of persistent upslope. Along with the passage of the shortwave comes that of the arctic cold front, allowing winds to begin shifting to the north-northwest. Simultaneously, the surface cyclone along the international border will slide to the east, continuing to deepen and become our primary low as it reaches the New England Coastline just inside the Gulf of Maine. A steepened pressure gradient will subsequently become established across our region with low-level frontogenesis increasing along and ahead of the front. This could lead to some isolated snow squalls developing late Friday night/early Saturday morning, though there is not high confidence in this detail of the forecast at this time. Part of the uncertainty relates to the lack of surface instability that is being indicated by the medium-range guidance at this time. Regardless, snow showers will persist into Saturday afternoon before completely scouring out in the face of increasing subsidence in the wake of the front. When all is said and done, snowfall accumulations look to range from about 0.5" to 2" with localized higher amounts of 3" to 4" potentially in some of the highest elevations of the Southern Adirondacks and Southern Greens.

KEY MESSAGE 2...

A prolonged period of dangerously cold conditions will consume eastern New York and western New England in the wake of the aforementioned arctic front. Not only will air temperatures be brutally cold, but a building high to the west and the still deepening, eastward-departing low will maintain a steepened pressure gradient across our region through Sunday making for gusty conditions as well. This will drive apparent temperatures, or wind chill values/"feels-like" temperatures, into dangerous territory from Saturday through potentially as late as Sunday night. It is not out of the question at this time for Friday night to also be dangerously cold, but this would likely not be as widespread given the later onset of snow and subsequent better insulation due to more extensive cloud cover and slower winds prior to the cyclogenesis of the surface low.

According to the latest NAEFS, 850hPa temperatures remain around 1.5 to 2.5 STDEVs below normal Friday night through Monday, translating to near surface temperatures that are between 2 and nearly 3 STDEVs below normal during the same period. The latest NBM Minimum Temperature QMD probabilities for subzero values across eastern New York and western New England are ~10-90% Friday night; ~40-100% Saturday night; ~30-100% Sunday night; and ~10-70% Monday night with the highest probabilities consistently located in areas of higher terrain. That said, especially Saturday night and Sunday night, higher probabilities are much more widespread and include large portions of the Mohawk Valley, Upper-Hudson Valley, Capital District, Mid-Hudson Valley, and lower terrain areas of western New England. Additionally, the latest LREF probabilities for apparent temperatures (wind chill values/"feels-like" temperatures) less than -10F range from ~40-90% Friday night; ~50-90% Saturday during the day; ~70-100% Saturday night; ~70-100% Sunday night; and ~20-70% Monday night.

At this point, we have high confidence in the occurrence of this arctic outbreak, but moderate confidence in the actual temperature and apparent temperature forecast. This stems in part from also needing to iron out the exact magnitude of the wind speeds during this time as well. But as lead time decreases, we will certainly gain more confidence in these finer details. And, given the high confidence in the occurrence of such a dangerous cold outbreak, we also have high confidence that Cold Weather Advisories and potentially Extreme Cold Watches/Warnings will be needed in the near future.

AVIATION /00Z WEDNESDAY THROUGH SUNDAY/

Through 00z Thursday...Flying conditions are VFR at all terminals as of 6:15 PM EST. VFR conditions continue through the first 3 hrs of the TAF period, but then isolated snow showers will be possible ahead of a cold front. Snow showers will generally be very light and quick-moving, but could still result in brief MVFR vsbys if they move over one of the terminals. Best chance is at ALB/PSF, followed by GFL. Not expecting any snow showers at POU. Snow showers end by 7- 9z, with VFR conditions and SCT to BKN mid-level clouds at ALB/GFL/POU through the remainder of the TAF period. At PSF, a period of MVFR cigs is expected late tonight through mid-morning tomorrow, but then the cloud bases should rise above 3000 ft with coverage of clouds also diminishing through the rest of the day. Will also note there remains a low probability for some patchy stratus/mist at GFL right around sunrise if cloud cover breaks up there, but current thinking is for enough mid-level cloud cover to prevent this. Winds will be light and variable through tonight, increasing to 5-10 kt tomorrow morning, with some gusts to around 20 kt at ALB/PSF from late morning through tomorrow evening.

Outlook...

Wednesday Night: No Operational Impact. NO SIG WX. Thursday: No Operational Impact. NO SIG WX. Thursday Night: No Operational Impact. NO SIG WX. Friday: Low Operational Impact. NO SIG WX. Friday Night: Moderate Operational Impact. Breezy. Likely SHSN. Saturday: Moderate Operational Impact. Windy With Gusts To 35 kts. Slight Chance of SHSN. Saturday Night: Moderate Operational Impact. Windy With Gusts To 30 kts. NO SIG WX. Sunday: Low Operational Impact. Breezy. NO SIG WX.

ALY WATCHES/WARNINGS/ADVISORIES

CT...None. NY...None. MA...None. VT...None.